1. Field of the Invention
The present invention relates to a magnetic sensor that includes a magnetic converging plate and is configured to detect magnetic fields in a vertical direction and a horizontal direction, and to a method of manufacturing the magnetic sensor.
2. Description of the Related Art
Hall elements allow non-contact position detection and non-contact angle detection as magnetic sensors, and are thus often used in various applications.
First, the principle of magnetic detection with the Hall elements is described. When a magnetic field is applied vertically to a current flowing through a substance, an electric field (Hall voltage) is generated in a direction vertical to both the current and the magnetic field. Thus, the typical Hall elements are configured to detect a vertical magnetic field component with a current caused to flow on a surface of a substrate (wafer).
In addition, it is known that the Hall elements can detect not only a vertical magnetic field but also a horizontal magnetic field in combination with a magnetic thin film formed of a material having high magnetic permeability, with the use of the magnetic thin film as a magnetic converging plate configured to change a direction of a magnetic flux to guide the magnetic flux to the Hall elements.
In order to realize a magnetic sensor that has a balanced ratio between vertical magnetic field sensitivity and horizontal magnetic field sensitivity and thus has a small variation in magnetic property, a positional relationship between the Hall elements and the magnetic converging plate is important (for example, see Japanese Patent Application Laid-open No. 2012-047708).
In order to reduce a variation in magnetic property due to an influence of a variation in position of the magnetic converging plate, there are a method involving patterning the magnetic converging plate on a Si substrate on which the Hall elements and a circuit are formed in advance through photolithography or the like, and a method involving forming the magnetic converging plate by plating (for example, see Japanese Patent Application Laid-open No. 2012-151285). An example is briefly described with reference to FIG. 2A to FIG. 2E.
First, as illustrated in FIG. 2A, a pair of Hall elements 2 is formed in spaced-apart relationship on a surface of a P-type semiconductor substrate 1. A protective film 3 serving as an insulator such as a polyimide film is formed on surfaces of the Hall elements 2 and the P-type semiconductor substrate 1.
Then, as illustrated in FIG. 2B, a base conductive layer 11 of a magnetic converging plate is formed on the protective film 3 serving as an insulator.
Next, as illustrated in FIG. 2C, a resist is applied on the base conductive layer 11, and a portion of the resist formed on a magnetic converging plate forming region is removed.
Then, as illustrated in FIG. 2D, the magnetic converging plate 10 is formed by plating in the region from which the resist is removed.
Finally, as illustrated in FIG. 2E, the remaining resist is removed, thereby being capable of forming the magnetic converging plate 10 in a desired region.
Further, there is also a method involving arranging, on a Si substrate on which the Hall elements and the circuit are formed, a structure for adjusting a position of a magnetic converging plate, to thereby improve accuracy of position adjustment and thus reduce a variation in magnetic property (for example, see Japanese Patent Application Laid-open No. 2003-130936).
When the magnetic converging plate is formed by plating and sputtering, in order to realize a reduction in coercive force and high magnetic permeability of a magnetic material, it is generally required to perform annealing at a high temperature equal to or higher than the Curie point. However, since annealing at such high temperature cannot be applied to the magnetic converging plate after the circuit and the Hall elements are formed, it is difficult to attain the magnetic converging plate having high magnetic permeability and low coercive force.
Further, the method involving arranging the structure for adjusting the position of the magnetic converging plate has a drawback that the number of processes increases due to additional processes such as forming the structure for position adjustment and removing the structure after the magnetic converging plate is arranged.